Phosphate Precipitation with Ferrous IronOf a number of methods available for phosphate removal from waste water, chemical precipitation (often called coagulation) using aluminum, ferric iron, ferrous iron and lime is considered to be the most economical. The objective of the present study has been two-fold: To evaluate the effects of pH and reactant concentration on the rate and efficiency of phosphate removal from synthetic and secondary effluent wastewaters and on the nature of the precipitates formed; and to compare the data on the Fe(II)-phosphate precipitation system with the available data for Fe(III)- and Al(III)-phosphate systems. Most of the experiments in the study were conducted on pure orthophosphate solutions and in the absence of dissolved oxygen. Only a limited number of tests were made of the use of ferrous iron for orthophosphate removal from wastewaters containing dissolved oxygen. |
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absence of dissolved activated sludge addition of Fe(II Al(III argon Atmosphere Reaction System bicarbonate bicarbonate alkalinity cation change in solution cipitates conducted Controlled Atmosphere Reaction dissolved oxygen Effect of pH effluent with Fe(II equilibrium constants Experiment 11 Experiments with Fe(II exposure to air Fe(II)-to-orthophosphate equivalence ratio ferrous ammonium sulfate ferrous iron ferrous phosphate flocculation hr of settling hydrolysis hydroxide indicates no measurements Initial orthophosphate concentration initial pH maximum orthophosphate removal membrane filters ments mg/l NaOH ortho ORTHOPHOSPHATE PRECIPITATION orthophosphate removal efficiency orthophosphate solutions containing oxidation of ferrous phos phosphate precipitation phosphate removal efficiency pickle liquor precipitates formed precipitates retained precipitation experiments PRECIPITATION FROM SECONDARY precipitation of orthophosphate Precipitation with Fe(II presence of dissolved pyro pyrophosphate ratio of 1.0 reactant removal reaction vessel residual reactant concentrations secondary effluent Settling Characteristics Settling Rate Studies soluble solution pH Table 11 tion titrator tripolyphosphate turbidity vivianite wastewater treatment x-ray diffraction